Effect of Oxalate and Urea upon Ultracentrifugation Properties of Raw and Heated Skimmilk Casein Micelles

Abstract

Casein micelles, sedimented from raw and heated skim milk by high speed centrifugation, were disaggregated and dissociated by combinations of oxalate, urea and phosphate buffer treatments, and examined by ultracentrifugation. Heating skim milk to temperatures of 120 C or less had only slight affect upon the ability of urea to dissociate casein micelles. However, heating skim milk at this and lower temperatures greatly reduced the ability of oxalate and phosphate buffer treatments to disaggregate casein micelles. A model was proposed which describes the native skim milk casein micelle in terms of its casein and ionic and colloidal inorganic constituents. A scheme was also presented for the disaggregation and dissociation mechanism of skim milk casein micelles to casein monomer subunits.